Add renewal info to license expiration warning banner
### Overview
The warning message we present when a license is expiring isn't particularly clear. We should make it more prescriptive and directive so customers understand what they need to do.
### Acceptance Criteria:
* Add link to https://about.gitlab.com/pricing/licensing-faq/#self-managed-gitlab
* Copy should say "Your license will expire in X days. For renewal instructions [view our Licensing and Subscription FAQ]."
issue